Looping through a result set

[venerable bede]

SQL Server 2008
I need to loop through a result set n times and calculate percentages.

Lets say my result contains one field and looks like :

Field1
=====
2
2
1
0

Lets say that my parameter "n" = 3.
I must loop through the result set and calculate what the percentages are for the numbers 1 through 3 and return these.
In the above example I would get
One = 25%, Two = 50%, 3= 0%, Unknown = 25%.

I have been looking at this all day and for the life of me cannot figure out how to achieve it .

Any help would be much welcomed.